This invention relates to the preparation of halohydroxypropyltrialkylammonium halides.
Halohydroxypropyltrialkylammonium halides are known to be useful as intermediates used in modification of natural and synthetic polymers, particularly in production of cationic polysaccharides, e.g. starch.
Halohydroxypropyltrialkylammonium halides are generally prepared by reaction of certain trialkylamines or their salts with epihalohydrins for instance by methods taught in European Patent Application No. 55,796 and U.S. Pat. Nos. 2,876,217: 3,135,788: 4,450,295 and 4,594,452. U.S. Pat. No. 2,876,217 discloses reactions of epihalohydrin and certain tertiary amines or salts in aqueous systems at a pH of at least about 5. Use of such a method results in a series of by-products, including unreacted epihalohydrins and 1,3-dihalo-2-propanol, which are preferably removed by careful purification by solvent extraction or vacuum distillation. European Patent Application No. 55,796 and U.S. Pat. No. 3,135,788 also disclose aqueous systems for similar reactions which require careful purification. U.S. Pat. No. 4,594,452 discloses the use of certain organic solvents which are solvents for epichlorohydrin and a trialkylammonium salt. U.S. Pat. No. 4,450,295 discloses certain combinations of aqueous and organic solvents for such reactions. These methods involve handling and removing a solvent material in addition to by-products. When the solvent is removed a solid product which readily deliquesces is produced. Generally, production of a solid product not only requires extra steps such as solvent removal and avoiding deliquescensce, but is also unnecessary because product halohydroxypropyltrialkylammonium halides are often sold commercially as aqueous solutions.
Alternatively, allyltrialkylammonium compounds are treated with such compounds as hypochlorous acid to form the corresponding chlorohydrins such as by the processes disclosed in U.S. Pat. Nos. 3,346,563: 3,532,751; and 3,558,501. Yield of by-products can be high as reported in U.S. Pat. No. 3,346,563, where about 30 percent by-product is noted.
Known methods of purifying chlorohydroxypropyltrialkylammonium chloride products include those taught in U.S. Pat. No. 2,876,217. These processes remove some by-products but frequently are ineffective in removing bis(trialkylammonium chloride)-2-hydroxypropanes (diquaternary compounds). Removal of diquaternary compounds generally requires processes such as fractional crystallization after solvent removal. Fractional crystallization is generally tedious and generally results in loss of product. Additional by-products which require careful separation include dihalopropanol (produced from epihalohydrin) and 2,3-epoxypropyltrialkylammonium chlorides (epoxy compounds).
Glycidyl quaternary ammonium salts have been prepared from the reaction of epihalohydrins with tertiary amines in the presence of a small quantity of 1,3-dihalohydrin as disclosed in Japanese Kokai 61-134383 (1986). Preferably, the dihalohydrin is present in an amount equivalent to 1-15 mole percent, more preferably 2-8 mole percent, relative to the tertiary amine. The purpose of the dihalohydrin is to reduce the amount of quaternary ammonium hydroxide by-product in the strongly alkaline solution containing the amine. The production of halohydroxypropyltrialkylammonium halides is generally preferred over the corresponding glycidyl compounds however, because the glycidyl compounds are relatively unstable and their purity can be greatly reduced during storage when compared to the halohydroxypropyltrialkylammonium halides.
It would be desirable to have a process of producing halohydroxypropyltrialkylammonium halides which avoids solids handling, has a simplified purification, and preferably, results in reduced production of dihalopropanol, epoxy and diquaternary by-products.